Durable EMI shielding film

ABSTRACT

A device or an enclosed area that can cause or is sensitive to electromagnetic interference (EMI) is shielded by at least partially surrounding the device or the area with a visible light-transmissive film comprising a flexible support, an extensible visible light-transmissive metal or metal alloy layer and a visible light-transmissive crosslinked polymeric protective layer, and optionally connecting at least one grounding electrode to the metal or metal alloy layer. The film has reduced susceptibility to fracture or corrosion compared to commercially available EMI shielding films, especially when bent or deformed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. application Ser. No.10/222,465, “Durable Transparent EMI Shielding Film”, filed Aug. 17,2002 now U.S. Pat. No. 6,818,291, as a continuation-in-part.

FIELD OF THE INVENTION

This invention relates to electrically conductive films suitable for usein electromagnetic interference (EMI) shielding applications.

BACKGROUND

EMI shielding films block the transmission of unwanted electromagneticenergy into or out of electronic equipment. A variety of conductivematerials can be used for this purpose. For applications in which it isnecessary to see through the shielding (e.g., to view a display),windows containing fine wire mesh and specialized transparent films havebeen used. Transparent EMI shields are also described in U.S. Pat. Nos.4,910,090 and 5,489,489 and in European Patent Application No. EP810452. Commercially available transparent EMI shielding films typicallyemploy a polymer substrate such as PET coated with a conductive oxidefilm (e.g., indium tin oxide) or with alternating coated layers of metal(e.g., silver) and conductive oxide. Representative commerciallyavailable transparent EMI shielding films include AgHT™-4 and AgHT™-8films (CP Films, Inc.), ALTAIR™ M and XIR™ transparent conductive film(Southwall Technologies) and WIN-SHIELD™ AgF8 film (Chomerics Divisionof Parker Hannifin Corporation).

Current commercially available EMI shielding films lack adequatedurability, contamination resistance or corrosion resistance. Forexample, the handling guidelines for film-based shields supplied by CPFilms, Inc. recommend that workers wear non-dusted latex gloves and facemasks when handling shielding films; caution that the conductive filmcoating is susceptible to attack by inorganic ions such as sodium,potassium and chloride, all of which are present on human fingers and insaliva; and recommend that if the film does become contaminated, itssurface should be cleaned with a non-linting clean room wipe dampened inisopropyl alcohol. These handling guidelines also caution against excessrubbing when wiping the coating, since it is very thin and somewhatfragile.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a process fortransparently shielding a device or enclosed area that can cause or issensitive to electromagnetic interference, comprising at least partiallysurrounding the device or area with a visible light-transmissive filmcomprising a flexible support, an extensible visible light-transmissivemetal or metal alloy layer and a visible light-transmissive crosslinkedpolymeric protective layer, and optionally connecting at least onegrounding electrode to the metal or metal alloy layer.

In a second aspect, the invention provides an electromagneticallyshielded article comprising a device or enclosed area that can cause oris sensitive to electromagnetic interference, wherein the device or areais at least partially surrounded with a visible light-transmissive filmcomprising a flexible support, an extensible visible light-transmissivemetal or metal alloy layer and a visible light-transmissive crosslinkedpolymeric protective layer, and optionally wherein at least onegrounding electrode is connected to the metal or metal alloy layer.

In a third aspect, the invention provides an electromagneticallyshielded article comprising a device or an enclosed area that can causeor is sensitive to electromagnetic interference, wherein the device orarea is at least partially surrounded with a visible light-transmissivefilm comprising a flexible support and extensible visiblelight-transmissive first and second metal or metal alloy layersseparated by a visible light-transmissive crosslinked polymeric layer.

The disclosed films and articles can have increased resistance todelamination, fracture or corrosion when formed or when subjected tobending, flexing, stretching, deforming operations or corrosiveconditions, yet still maintain adequate electrical conductivity, andhence good EMI shielding performance. Preferably, the metal or metalalloy layers are substantially continuous over substantial areas of thefilm, i.e., over portions of the film where EMI shielding, heating, orlike functionality is desired. In some embodiments, the metal or metalalloy layers can be completely continuous over the entire film; in otherembodiments the metal or metal alloy layers can be patterned to define alimited number of apertures, holes, or channels for desiredfunctionality (e.g. to provide one or more frequency selective surfacesor distinct, electrically conductive pathways).

These and other aspects of the invention will be apparent from thedetailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic perspective view of a disclosedelectromagnetically shielded article;

FIG. 2 through FIG. 5 are schematic cross-sectional views of disclosedfilms;

FIG. 6A is a schematic view of an apparatus for manufacturing thedisclosed films;

FIG. 6B is an enlarged partial cross-sectional view of a disclosedcompound-curved article;

FIG. 6C is a perspective view of a portion of a disclosedcompound-curved article;

FIG. 6D and FIG. 6E are enlarged partial cross-sectional views ofdisclosed compound-curved articles;

FIG. 6F is a partial schematic diagram of a corrugating apparatus thatcan be used to prepare curved articles;

FIG. 6G and FIG. 6H are perspective views of corrugated curved articles;

FIG. 7 and FIG. 8 are graphs showing transmittance and reflectance forthe films of Example 1 and Example 2, respectively;

FIG. 9 through FIG. 11 are graphs showing conductance vs. strain for thefilms of Example 4, Example 5 and Example 11, respectively;

FIG. 12 through FIG. 15 are graphs showing transmittance and reflectancefor the films of Example 12, Example 20, Example 21 and Example 22,respectively; and

FIG. 16 is a schematic plan view of a compound curved shape formed inExample 24.

Like reference symbols in the various figures of the drawing indicatelike elements. The elements in the drawing are not to scale.

DETAILED DESCRIPTION

By using words of orientation such as “atop”, “on”, “uppermost” and thelike for the location of various layers in the disclosed films orarticles, we refer to the relative position of one or more layers withrespect to a horizontal support layer. We do not intend that the filmsor articles should have any particular orientation in space during orafter their manufacture.

By a “light-transmissive” support, layer, film or article, we mean thatthe support, layer, film or article has an average transmission, T, in aspectral range of interest of at least about 20%, measured along thenormal axis. By a “visible light-transmissive” support, layer, film orarticle, we mean that the support, layer, film or article has atransmission, T_(vis), in the visible portion of the spectrum, of atleast about 20%, measured along the normal axis. By an“infrared-reflective” support, layer, film or article, we mean that thesupport, layer, film or article reflects at least about 50% of light ina band at least 100 nm wide in a wavelength region from about 700 nm toabout 2000 nm, measured at a near-normal angle (e.g., at about a 6°angle of incidence). By “light” we mean solar radiation.

By a “flexible” support, layer, film or article, we mean that thesupport, layer, film or article can be bent 30° from its originalposition (without requiring folding or creasing) and released to recoverat least part of its original shape without loss of electricalcontinuity and without forming visible discontinuities as detected bythe naked eye at a distance of about 0.25 meters.

By a “metal layer” we mean a metal or metal alloy layer.

By an “extensible” metal layer we refer to a layer that whenincorporated into a light-transmissive film or article can be stretchedby at least 3% in an in-plane direction without loss of electricalcontinuity and without forming visible discontinuities in the surface ofthe metal layer as detected by the naked eye at a distance of about 0.25meters.

By a “crosslinked” polymer, we mean a polymer in which polymer chainsare joined together by covalent chemical bonds, usually via crosslinkingmolecules or groups, to form a network polymer. A crosslinked polymer isgenerally characterized by insolubility, but may be swellable in thepresence of an appropriate solvent. The term “polymer” includeshomopolymers and copolymers, as well as homopolymers or copolymers thatmay be formed in a miscible blend, e.g., by coextrusion or by reaction,including, e.g., transesterification. The term “copolymer” includes bothrandom and block copolymers.

By a “non-planar” support, layer, film or article, we mean that thesupport, layer, film or article has a continuous, intermittent,unidirectional or compound curvature. By a support, layer, film orarticle that is “compound curved” or has “compound curvature”, we meanthat a surface of the support, layer, film or article curves in twodifferent, non-linear directions from a single point.

By a “self-supporting” compound curved support, layer, film or article,we mean that the support, layer, film or article has sufficient rigidityto substantially maintain its shape when placed on a horizontal surfaceand when held by hand at one end and allowed to hang vertically.

By a “permanently deformed compound curved region” of a support, layer,film or article, we mean that a surface of the support, layer, film orarticle includes a non-planar region having compound curvature whoseshape substantially persists when the support, layer, film or article isheld taut by hand at two opposing ends so that apparent slackness isremoved.

By “optically clear” we refer to a film or article in which there is anabsence of visibly noticeable haze or flaws as detected by the naked eyeat a distance of about 1 meter, preferably about 0.5 meters.

Referring to FIG. 1, medical device 10 is partially shielded from EMI bymetal housing 12. Information display 14 on housing 12 is covered with atransparent EMI shielding film 16. Metallic bezel 18 surrounds film 16and serves as a grounding electrode that electrically connects theentire perimeter of film 16 to housing 12. Film 16 provides EMIshielding for the remainder of device 10 not already shielded by housing12.

Referring to FIG. 2, a film usable as an EMI shield is shown generallyat 110. Film 110 includes flexible support 112 made of a visiblelight-transparent plastic film such as polyethylene terephthalate(“PET”). Extensible visible light-transparent metal layer 116 made ofsilver lies atop support 112. Protective layer 122 made of a crosslinkedacrylate polymer lies atop metal layer 116. Metal layer 116 is groundedvia electrode 124.

In FIG. 3, another film usable as an EMI shield is shown generally at130. Film 130 resembles film 110, but includes a base coat layer 132made from crosslinked acrylate polymer between support 112 and metallayer 116.

In FIG. 4, a film usable as an EMI shield is shown generally at 140.Film 140 resembles film 110, but includes Fabry-Perot interference stack114 atop support 112. Stack 114 includes first visible light-transparentmetal layer 116, a visible light-transparent spacing layer 118 made of acrosslinked acrylate polymer and second visible light-transparent metallayer 120 made of silver. The thicknesses of the metal layers 116 and120 and the intervening crosslinked polymeric layer 118 are carefullychosen so that metal layers 116 and 120 are partially reflective andpartially transmissive. Spacing layer 118 has an optical thickness(defined as the physical thickness of layer times its in-plane index ofrefraction) to achieve the center of the desired pass band fortransmitted light. Light whose wavelength is within the pass band ismainly transmitted through the thin metal layers 116 and 120. Lightwhose wavelength is above the pass band is mainly reflected by the thinmetal layers 116 and 120 or canceled due to destructive interference.Spacing layer 118 also serves as a protective layer for first metallayer 116.

In FIG. 5, another disclosed film is shown generally at 150. Film 150resembles film 140, but includes base coat layer 132 between support 112and metal layer 116, and a second grounded electrode 124.

A variety of visible light-transparent supports can be employed.Preferred supports have a visible light transmission of at least about70% at 550 nm. Particularly preferred supports are flexible plasticmaterials including thermoplastic films such as polyesters (e.g., PET),polyacrylates (e.g., polymethyl methacrylate), polycarbonates,polypropylenes, high or low density polyethylenes, polyethylenenaphthalates, polysulfones, polyether sulfones, polyurethanes,polyamides, polyvinyl butyral, polyvinyl chloride, polyvinylidenedifluoride and polyethylene sulfide; and thermoset films such ascellulose derivatives, polyimide, polyimide benzoxazole and polybenzoxazole. The support can also be a multilayer optical film (“MOF”)such as those described in U.S. Patent Application Publication No. US2002/0154406 A1, or a MOF coated with at least one crosslinked polymericlayer and metal layer such as those described in copending applicationSer. No. 10/222,473, filed Aug. 17, 2002 and entitled “ENHANCED HEATMIRROR FILMS”, incorporated herein by reference. Supports made of PETand MOF are especially preferred. Preferably the support has a thicknessof about 0.01 to about 1 mm. The support may however be considerablythicker, for example when a self-supporting article is desired. Sucharticles can conveniently also be made by forming one or more metallayers and one or more cross-linked polymeric layers of atop a flexiblesupport, and laminating or otherwise joining the flexible support to athicker, inflexible or less flexible supplemental support as describedin more detail below.

The metal layer 116 can be made from a variety of materials. Preferredmetals include elemental silver, gold, copper, nickel and chrome, withsilver being especially preferred. Alloys such as stainless steel ordispersions containing these metals in admixture with one another orwith other metals also can be employed. When additional metal layers areemployed, they can be the same as or different from one another, andneed not have the same thickness. Preferably the metal layer or layersare sufficiently thick so as to remain continuous if elongated by morethan 3% in an in-plane direction, and sufficiently thin so as to ensurethat the film and articles employing the film will have the desireddegree of EMI shielding and light transmission. Preferably the physicalthickness (as opposed to the optical thickness) of the metal layer orlayers is about 3 to about 50 nm, more preferably about 4 to about 15nm. Typically the metal layer or layers are formed by deposition on theabove-mentioned support using techniques employed in the filmmetallizing art such as sputtering (e.g., cathode or planar magnetronsputtering), evaporation (e.g., resistive or electron beam evaporation),chemical vapor deposition, plating and the like.

The smoothness and continuity of the first metal layer and its adhesionto the support preferably are enhanced by appropriate pretreatment ofthe support. A preferred pretreatment regimen involves electricaldischarge pretreatment of the support in the presence of a reactive ornon-reactive atmosphere (e.g., plasma, glow discharge, corona discharge,dielectric barrier discharge or atmospheric pressure discharge);chemical pretreatment; flame pretreatment; or application of anucleating layer such as the oxides and alloys described in U.S. Pat.Nos. 3,601,471 and 3,682,528. These pretreatments may help ensure thatthe surface of the support will be receptive to the subsequently appliedmetal layer. Plasma pretreatment is particularly preferred. A furtherparticularly preferred pretreatment regimen involves coating the supportwith an inorganic or organic base coat layer such as layer 132 above,optionally followed by further pretreatment using plasma or one of theother pretreatments described above. Organic base coat layers, andespecially base coat layers based on crosslinked acrylate polymers, areespecially preferred. Most preferably, the base coat layer is formed byflash evaporation and vapor deposition of one or moreradiation-crosslinkable monomers (e.g., acrylate monomers, optionallycombined with a suitable photoinitiator), followed by crosslinking insitu (using, for example, an electron beam apparatus, UV light source,electrical discharge apparatus or other suitable device), as describedin U.S. Pat. Nos. 4,696,719, 4,722,515, 4,842,893, 4,954,371, 5,018,048,5,032,461, 5,097,800, 5,125,138, 5,440,446, 5,547,508, 6,045,864,6,231,939 and 6,214,422; in published PCT Application No. WO 00/26973;in D. G. Shaw and M. G. Langlois, “A New Vapor Deposition Process forCoating Paper and Polymer Webs”, 6th International Vacuum CoatingConference (1992); in D. G. Shaw and M. G. Langlois, “A New High SpeedProcess for Vapor Depositing Acrylate Thin Films: An Update”, Society ofVacuum Coaters 36th Annual Technical Conference Proceedings (1993); inD. G. Shaw and M. G. Langlois, “Use of Vapor Deposited Acrylate Coatingsto Improve the Barrier Properties of Metallized Film”, Society of VacuumCoaters 37th Annual Technical Conference Proceedings (1994); in D. G.Shaw, M. Roehrig, M. G. Langlois and C. Sheehan, “Use of EvaporatedAcrylate Coatings to Smooth the Surface of Polyester and PolypropyleneFilm Substrates”, RadTech (1996); in J. Affinito, P. Martin, M. Gross,C. Coronado and E. Greenwell, “Vacuum deposited polymer/metal multilayerfilms for optical application”, Thin Solid Films 270, 43-48 (1995); andin J. D. Affinito, M. E. Gross, C. A. Coronado, G. L. Graff, E. N.Greenwell and P. M. Martin, “Polymer-Oxide Transparent Barrier Layers”,Society of Vacuum Coaters 39th Annual Technical Conference Proceedings(1996). If desired, the base coat can also be applied using conventionalcoating methods such as roll coating (e.g., gravure roll coating) orspray coating (e.g., electrostatic spray coating), then crosslinkedusing, for example, UV radiation. The desired chemical composition andthickness of the base coat layer will depend in part on the nature ofthe support. For example, for a PET support, the base coat layerpreferably is formed from an acrylate monomer and typically will have athickness of only a few nanometers up to about 2 micrometers.

The adhesion of the first metal layer to a base coat layer can befurther improved by including an adhesion-promoting or anticorrosionadditive in the base coat layer. This may affect the surface energy orother relevant characteristics of the interface between the base coatlayer and the first metal layer. Suitable adhesion-promoting oranticorrosion additives include mercaptans, thiol-containing compounds,acids (such as carboxylic acids or organic phosphoric acids), triazoles,dyes and wetting agents. Ethylene glycol bis-thioglycolate (described inU.S. Pat. No. 4,645,714) is a particularly preferred additive. Theadditive preferably is present in amounts sufficient to obtain thedesired degree of increased adhesion, without causing undue oxidation orother degradation of the first metal layer.

A crosslinked polymeric layer lies atop the first metal layer, andserves as a protective corrosion-resistant topcoat 122 if no other metallayers are present and as a protective layer and spacing layer such aslayer 118 if additional metal layers are employed. Stacks containing 2,3 or 4 metal layers provide desirable characteristics for someapplications. Stacks containing 2 to 4 metal layers in which each of themetal layers has a crosslinked polymeric layer adjacent to each of itsfaces are especially preferred. Exemplary films containing Fabry-Perotoptical interference stacks are described in copending application Ser.No. 10/222,466, filed Aug. 17, 2002 and entitled “POLYMER-METAL INFRAREDINTERFERENCE FILTER”, incorporated herein by reference, and in the abovementioned copending application Ser. No. 10/222,473. Use of acrosslinked polymeric spacing layer between metal layers renders thefilm and its metal layers more readily extensible while reducing damageto the metal layers.

The crosslinked polymeric layer can be formed from a variety of organicmaterials. Preferably the polymeric layer is crosslinked in situ atopthe first metal layer. If desired, the polymeric layer can be appliedusing conventional coating methods such as roll coating (e.g., gravureroll coating) or spray coating (e.g., electrostatic spray coating), thencrosslinked using, for example, UV radiation. Most preferably thepolymeric layer is formed by flash evaporation, vapor deposition andcrosslinking of a monomer as described above for base coat layer 132.Volatilizable (meth)acrylate monomers are preferred for use in such aprocess, with volatilizable acrylate monomers being especiallypreferred. Preferred (meth)acrylates have a molecular weight in therange of about 150 to about 600, more preferably about 200 to about 400.Other preferred (meth)acrylates have a value of the ratio of themolecular weight to the number of acrylate functional groups permolecule in the range of about 150 to about 600 g/mole/(meth)acrylategroup, more preferably about 200 to about 400 g/mole/(meth)acrylategroup. Fluorinated (meth)acrylates can be used at higher molecularweight ranges or ratios, e.g., about 400 to about 3000 molecular weightor about 400 to about 3000 g/mole/(meth)acrylate group. Coatingefficiency can be improved by cooling the support. Particularlypreferred monomers include multifunctional (meth)acrylates, used aloneor in combination with other multifunctional or monofunctional(meth)acrylates, such as hexanediol diacrylate, ethoxyethyl acrylate,phenoxyethyl acrylate, cyanoethyl(mono)acrylate, isobornyl acrylate,isobornyl methacrylate, octadecyl acrylate, isodecyl acrylate, laurylacrylate, beta-carboxyethyl acrylate, tetrahydrofurfuryl acrylate,dinitrile acrylate, pentafluorophenyl acrylate, nitrophenyl acrylate,2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate,2,2,2-trifluoromethyl(meth)acrylate, diethylene glycol diacrylate,triethylene glycol diacrylate, triethylene glycol dimethacrylate,tripropylene glycol diacrylate, tetraethylene glycol diacrylate,neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate,polyethylene glycol diacrylate, tetraethylene glycol diacrylate,bisphenol A epoxy diacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane triacrylate, ethoxylated trimethylol propane triacrylate,propylated trimethylol propane triacrylate,tris(2-hydroxyethyl)-isocyanurate triacrylate, pentaerythritoltriacrylate, phenylthioethyl acrylate, naphthloxyethyl acrylate, IRR-214cyclic diacrylate from UCB Chemicals, epoxy acrylate RDX80095 fromRad-Cure Corporation, and mixtures thereof. A variety of other curablematerials can be included in the crosslinked polymeric layer, e.g.,vinyl ethers, vinyl naphthylene, acrylonitrile, and mixtures thereof.The physical thickness of the crosslinked polymeric layer will depend inpart upon its refractive index and in part upon the desired opticalcharacteristics of the film (e.g., on whether the film containsadditional metal layers). For use in an infrared-rejecting EMI shieldingfilm containing a Fabry-Perot stack, the crosslinked polymeric layertypically will have a refractive index of about 1.3 to about 1.7, andpreferably will have an optical thickness of about 75 to about 350 nm,more preferably about 100 to about 275 nm and a corresponding physicalthickness of about 45 to about 270 nm, more preferably about 60 to about210 nm.

The smoothness and continuity of the crosslinked polymeric layer and itsadhesion to the first metal layer preferably are enhanced by appropriatepretreatment of the first metal layer prior to application of thecrosslinked polymeric layer, or by inclusion of a suitable additive inthe crosslinked polymeric layer. Preferred pretreatments include thesupport pretreatments described above, with plasma pretreatment of thefirst metal layer being particularly preferred. Preferred additives forthe crosslinked polymeric layer include the base coat layer additivesdescribed above.

The smoothness and continuity of any additionally applied metal layersand their adhesion to an underlying crosslinked polymeric layerpreferably are enhanced by appropriate pretreatment of the crosslinkedpolymeric layer prior to application of the additionally applied metallayer, or by inclusion of a suitable additive in the crosslinkedpolymeric layer. Preferred pretreatments include the supportpretreatments described above, with plasma pretreatment of thecrosslinked polymeric layer being particularly preferred. Preferredadditives for the crosslinked polymeric layer include the base coatlayer additives described above.

Surprisingly, we have also discovered that when one or both of theabove-described pretreatments is employed, and when one or more of theabove-described base coat layer additives is incorporated into themonomer mixture used for forming the spacing layer(s), the resistance ofthe metal layer(s) to corrosion under the influence of an electricalcurrent is markedly enhanced. Plasma treatment is a preferredpretreatment, with a nitrogen plasma being especially preferred.Ethylene glycol bis-thioglycolate is a preferred additive forincorporation into the monomer mixture.

Various functional layers or coatings can be added to the EMI shieldingfilm to alter or improve its physical or chemical properties,particularly at the surface of the film. Such layers or coatings caninclude, for example, low friction coatings or slip particles to makethe film easier to handle during film manufacturing; particles to adddiffusion properties to the film or to prevent wet-out or Newton's ringswhen the film is placed next to another film or surface; antireflectionlayers to prevent glare when the EMI shielding film is applied to theface of an information display; antistatic coatings; abrasion resistantor hardcoat materials; anti-fogging materials; magnetic or magneto-opticcoatings or films; adhesives such as pressure sensitive adhesives or hotmelt adhesives; primers to promote adhesion to adjacent layers; lowadhesion backsize materials for use when the film is to be used inadhesive roll form; liquid crystal panels; electrochromic orelectroluminescent panels; photographic emulsions; prismatic films andholographic films or images. Additional functional layers or coatingsare described, for example, in published PCT Application Nos. WO97/01440, WO 99/36262, and WO 99/36248. The functional layers orcoatings can also include shatter resistant, anti-intrusion, orpuncture-tear resistant films and coatings, for example, the functionallayers described in published PCT Application No. WO 01/96115.Additional functional layers or coatings can include vibration-dampingfilm layers such as those described in published PCT Application No. WO98/26927 and U.S. Pat. No. 5,773,102, and barrier layers to provideprotection or to alter the transmissive properties of the film towardsliquids such as water or organic solvents or towards gases such asoxygen, water vapor or carbon dioxide. These functional components canbe incorporated into one or more of the outermost layers of the EMIshielding film, or they can be applied as a separate film or coating orincluded in a supplemental support.

For some applications, it may be desirable to alter the appearance orperformance of the EMI shielding film, such as by laminating a dyed filmlayer to the film, applying a pigmented coating to the surface of thefilm, or including a dye or pigment in one or more of the materials usedto make the film. The dye or pigment can absorb in one or more selectedregions of the spectrum, including portions of the infrared, ultravioletor visible spectrum. The dye or pigment can be used to complement theproperties of the film, particularly where the film transmits somefrequencies while reflecting others. A particularly useful pigmentedlayer that can be employed in the EMI shielding films is described inpublished PCT Application No. WO 2001/58989. This layer can belaminated, extrusion coated or coextruded as a skin layer on the film.The pigment loading level can be varied between about 0.01 and about1.0% by weight to vary the visible light transmission as desired. Theaddition of a UV absorptive cover layer can also be desirable in orderto protect any inner layers of the film that may be unstable whenexposed to UV radiation. The EMI shielding film can also be treatedwith, for example, inks or other printed indicia such as those used todisplay product identification, orientation information, advertisements,warnings, decoration, or other information. Various techniques can beused to print on the EMI shielding film, such as, for example, screenprinting, inkjet printing, thermal transfer printing, letterpressprinting, offset printing, flexographic printing, stipple printing,laser printing, and so forth, and various types of ink can be used,including one and two component inks, oxidatively drying and UV-dryinginks, dissolved inks, dispersed inks, and 100% ink systems.

The EMI shielding films can be oriented and optionally heat set underconditions sufficient to assist the film in conforming withoutsubstantial wrinkling to a non-planar substrate. This is especiallyuseful when a non-planar substrate to which an EMI shielding film is tobe laminated has a known shape or curvature, and especially when thelaminate has a known severe compound curvature. By individuallycontrolling the shrinkage of the EMI shielding film or substrate in eachin-plane direction, the EMI shielding film can be caused to shrink in acontrolled fashion during lamination, especially during nip rolllamination. Further details regarding techniques for manufacturing MOFsupports having targeted shrinkage properties are described in publishedPCT Application No. WO 01/96104.

An apparatus 180 that can conveniently be used to manufacture thedisclosed films is shown in FIG. 6A. Powered reels 181 a and 181 b movesupporting web 182 back and forth through apparatus 180.Temperature-controlled rotating drums 183 a and 183 b, and idlers 184 a,184 b, 184 c, 184 d and 184 e carry web 182 past metal sputteringapplicator 185, plasma pretreater 186, monomer evaporator 187 and E-beamcrosslinking apparatus 188. Liquid monomer 189 is supplied to evaporator187 from reservoir 190. Successive layers can be applied to web 182using multiple passes through apparatus 180. Apparatus 180 can beenclosed in a suitable chamber (not shown in FIG. 6A) and maintainedunder vacuum or supplied with a suitable inert atmosphere in order todiscourage oxygen, water vapor, dust and other atmospheric contaminantsfrom interfering with the various pretreatment, monomer coating,crosslinking and sputtering steps.

The metal layer or layers of the EMI shielding film preferably areconnected to at least one grounding electrode such as electrode 124 inFIG. 2. The grounding electrode(s) can be connected to the metallayer(s) before or after the EMI shielding film is joined to othermaterials or to a device requiring EMI shielding. Grounding electrodescan be formed using masking, plating and other printed circuitrytechniques that will be familiar to those skilled in the art, or formedusing metallic strips, wires, conductive paints and other connectionsthat will likewise be familiar to those skilled in the art. 3M™Conductive Tapes 9703 and 9713 (3M, St. Paul Minn. are particularlypreferred grounding electrodes. These tapes contain fibers or particlesthat penetrate the outermost crosslinked polymer layer and provide anelectrical connection to the underlying metal layer. Appropriate busbarscan be employed with such tapes when two or more metal layers are to beconnected in series or in parallel.

In another embodiment, the metal layer need not be grounded. Althoughless preferred, such an embodiment does provide EMI shielding viareflection, and can be used for applications where lower levels of EMIshielding can be tolerated. Applications for such ungrounded EMIshielding films include testing facilities, security/secure rooms andantennae components.

In an EMI shielded article, preferably the majority and most preferablythe entire EMI shielding film perimeter is connected to the groundingelectrode(s). The grounding electrode(s) normally are connected orbonded to the device requiring EMI shielding or to a housing (e.g., anontransparent housing) surrounding the device.

When the EMI shielding film contains multiple metal layers, one or moreof the layers can be used for EMI shielding and one or more of theremaining layers can be used for a purpose other than EMI shielding,e.g., for heating, intrusion detection, touch detection infraredrejection and decorative or other optical purposes. Heating filmscontaining multiple metal layers are described in copending applicationSer. No. 10/222,449, filed Aug. 17, 2002 and entitled “FLEXIBLEELECTRICALLY CONDUCTIVE FILM”, incorporated herein by reference. The EMIshielding films can also be used for purposes where EMI shielding is notrequired, e.g., for heating, intrusion detection, touch detection,infrared rejection and decorative or other optical purposes without adeliberate EMI shielding role. Thus other uses for the EMI shieldingfilms and articles include electrically heated articles,electrode-containing articles, barrier articles, security articles,decorative articles and license plates.

The EMI shielding films and articles can be flexible or self-supporting.Fabrication of a self-supporting article can be made easier bylaminating or otherwise joining the film to a suitable supplementalsupport or other substrate. Typical supplemental support or substratematerials include glazing materials such as glass (which may beinsulated, tempered, laminated, annealed, or heat strengthened, and informs including sheets and molded articles), metals (which may belaminated, annealed, or heat strengthened, and in forms includingcontinuous or perforated sheets, mesh, slabs and molded articles) andplastics (which may be laminated, annealed or heat treated, and in formsincluding continuous or perforated sheets, woven or nonwoven mesh, slabsand molded articles). The EMI shielding films are especially useful innon-planar configurations or in connection with non-planar substrates,especially those having a compound curvature, including non-planarpanels or molded articles made of glass, metal, plastic materials suchas the support materials recited above and other suitable materials.Such non-planar configurations can often be obtained through deliberatedeformation of the EMI shielding film. For brevity, the word “preform”can be used to describe EMI shielding films or articles embodying theEMI shielding film that are intended to be subjected to a deformingoperation. The deforming operation may for example alter at least onesurface of the preform from the uniformly smooth, planar-surfaces theEMI shielding film typically has when initially fabricated. Thedeforming operation typically converts a generally smooth,planar-surfaced region of the preform to a region havingthree-dimensional characteristics. The deforming operation can employheat to improve the working qualities of the preform and other measuressuch as pressure, vacuum, molds, etc. For example, one preferreddeformation operation employs thermoforming, including the various formsof vacuum or pressure molding/forming, plug molding, injection molding,etc. The preform can be adhered to, stretched or otherwise deformed overa non-planar substrate (e.g., a compound curved substrate). The preformcan be embossed or otherwise deliberately reshaped. Drawing orstretching of the preform may also be employed to impart a permanentlydeformed compound curved region to the preform. Those skilled in the artwill appreciate that a variety of other fabrication techniques can beused to impart intentional deformation to the preform.

The deformation can include relatively small deformations such as thoseexperienced when embossing the film, up to larger scale deformationssuch as those experienced when molding or thermoforming the film. Thepreform preferably is capable of adopting a non-planar configurationwithout substantial cracking or creasing. The thus-deformed film orarticle can have a variety of configurations. One such configuration isdepicted in FIG. 6B, where preform 200 includes a first major surface202 and a second major surface 204 deformed in selected regions 206 and208. Selected region 206 is a depression in first major surface 202 andselected region 208 is a raised area in second major surface 208, and inthis instance these two regions coincide. The generally smooth, planarportions of preform 200 surrounding regions 206 and 208 define anundeformed thickness t₀. The selected regions 206 and 208 define adeformed thickness t_(f). In some instances it may be desirable that theratio t₀:t₁ be at least about 1.1:1, more preferably at least about1.5:1, yet more preferably at least about 1.75:1, and even morepreferably at least about 2:1.

FIG. 6C and FIG. 6D illustrate a more extreme deformation outcome.Article 210 can be considered an example of a deep draw deformationoperation. Article 210 includes a first major surface 212 and a secondmajor surface 214 along with a plurality of selected areas in which thepreform has been deformed to provide depressed areas 216 and openings220 formed in the first major surface 212 and raised areas 218 formed onthe second major surface 214. The depressed areas 216 include openings220, curved regions 222 and 224 having successively lower radii ofcurvature, and deeply drawn sidewalls 226. The deformation can becharacterized by the aspect ratio of the average width w of thedepressed areas 216 (as measured across opening 220) to the averagedepth d of the depressed areas 216 (as measured from the first majorsurface 212). For a noncircular opening 220 it is preferred that thewidth w be measured across its narrowest dimension. In some instances itmay be preferable that the depressed areas 216 have an aspect ratio w:dof about 10:1 or less, more preferably 2:1 or less, even more preferablyabout 1:1 or less, and still more preferably about 0.5:1 or less. Theextent of deformation can if desired be measured in absolute terms. Forsome instances it may be preferred that the depth d be at least about0.1 millimeter or more, more preferably at least about 1 millimeter ormore, and even more preferably at least about 10 millimeters or more. Itwill be understood that where the depth d approaches or exceeds thethickness of the preform, it becomes more likely that a raised area 218will be formed on the second major surface 214.

Measurement of the depth d of the depressed areas 216 formed in thefirst major surface 212 is not limited to those instances in which thefirst major surface is planar. Turning now to FIG. 6E, a deformedpreform 230 is depicted in a curved configuration. Preform 230 includesa depressed area 232 formed on the first major surface 234, acorresponding raised area 238 on the second major surface 236, areas oflow radius of curvature 240 and 242 and deeply drawn sidewalls 244. Thedepth d of depressed area 232 will preferably be measured from thegeometric surface defined generally by the first major surface 234 andwill typically be the largest depth from that geometric surface.

If the EMI shielding film includes a polymeric spacing layer betweenfirst and second metal layers, the spacing layer may undergo a reductionin thickness due to the deformation operation. In such instances thepolymeric spacing layer thickness may be generally lower at regions ofthe article that have experienced a high level of strain in thedeformation process and generally higher at regions of the article thathave experienced little or no strain during the deformation process.

Although not wishing to be bound by theory, it is believed that articlesformed by the disclosed processes undergo changes that are reflected inthe structures resulting from the process. A planar film comprising athermoplastic substrate, at least one metal or metal alloy layer, and atleast one crosslinked polymeric layer is deformed by the describedprocesses of embossing, extending, or thermoforming or the like toconform to a bent, curved, or compound curved shape. As a result of thisprocess, the metal or metal alloy layer may be elongated in some regionsand may be compressed in other regions. A material property that iscommonly measured is the elongation to break, which represents theamount that a material can be stretched (measured by strain) before thematerial undergoes cohesive failure (i.e. breakage). The determinationof whether a layer is compressed or elongated during the deformationprocess can be described by the spatial relation of the layer to theneutral plane of the original planar film, as described in U.S. Pat. No.4,888,061. Preferably, the metal or metal alloy layers are located nearthe neutral plane of the film. Material located on the neutral plane ofthe film is not subjected to stress as a result of deformation, and nostrain of the film results. Depending on the relative orientation of thedeformation, a material layer located above or below the neutral planewill either undergo compression or elongation. For example, the preformplanar film described above, will generally have a neutral plane withinthe substrate, and the metal or metal alloy layer, and the associatedtransparent crosslinked polymer layer, will be located a distance fromthis neutral plane. When the planar film is deformed such that the metalcontaining layer is between the neutral plane and the outside edge of aradius of curvature, the metal containing layer is elongated;conversely, when the metal containing layer is between the neutral planeand the inside edge of a radius of curvature, the metal containing layeris compressed. In a like manner, the relative thickness of each of thelayers in the planar film may be changed relative to the originalthickness, depending on whether the layers are formed under compressionor tension (which causes elongation). The elongation to break of themetal containing layer is dependent upon whether the layer has beencompressed or elongated. Compared to the elongation to break of theoriginal planar film, a metal containing layer which has been elongatedduring the deformation process will have a lower elongation to break(i.e. the layer can withstand much less stress before cohesive failure);additionally, the thickness of each of the layers in the film can bereduced during this deformation. In contrast, a metal-containing layerwhich has been compressed, has a higher elongation to break than theplanar film; additionally, the thickness of each of the layers in thefilm can be increased during this deformation.

FIG. 6F shows a partial view of a device 250 for corrugating a preformusing first and second generally cylindrical corrugating members orrollers 252 and 254 each having an axis and a multiplicity of spacedridges 256 and 258 respectively defining the periphery of corrugatingmembers 252 and 254. The spaces between ridges 256 and 258 are adaptedto receive the preform 260 in meshing relationship between corrugatingmembers 252 and 254. The arrangement also includes appropriate devicesfor rotating at least one of the corrugating members 252 or 254 and forfeeding or taking up the preform 260 so that the preform 260 will begenerally deformed to the shape defined by the periphery of the firstcorrugating member 252. Process parameters that influence thethree-dimensional configuration and in some instances the decorativeappearance of the resulting corrugated films include the temperatures ofthe corrugating rollers, the nip pressure between the corrugatingrollers, the diameter of the corrugating rollers, the line speed, andthe shape and spading of the ridges 256 and 258.

An undulated structure 280 that can be produced using such a corrugationprocess is shown in FIG. 6G. The undulations may be characterized byarcuate portions 282, valley portions 284, and intermediate portions 286and 288 which connect the arcuate portions to the valley portions. Whilethe undulations shown in FIG. 6G are sinusoidal in shape, it should berecognized that the corrugation process may create undulations of manyother desired shapes, such as those in corrugated article 290 shown inFIG. 6H. In addition, the corrugates need not extend the full width oralong the width of the preform. Rather, they may extend for any desiredlength and in any direction in the plane or general curvature of thepreform.

Those skilled in the art will recognize that a wide variety of preformsand deforming techniques may be employed to provide a wide variety ofpermanently deformed films and articles.

Assembly of the EMI shielding films or articles in a completed device oradjacent to an enclosed area can be carried out using techniques thatwill be familiar to those skilled in the art. For example,representative construction details for EMI shielding windows can befound in The Design of Shielded Enclosures: Cost-Effective Methods toPrevent EMI, by Louis T. Gnecco (Newnes Publishing:Butterworth-Heinemann, Boston, 2000). Additional EMI shielding materialssuch as gaskets, tapes, fabrics, foams or other materials may beemployed in combination with the EMI shielding films or articles.Representative EMI shielding equations and techniques for using suchother materials are described in the book cited above; in A HandbookSeries on Electromagnetic Interference and Compatibility (InterferenceControl Technologies, Inc., Gainesville, Va., 1988), especially Volume3: Electromagnetic Shielding, by Donald R. J. White and MichelMardiguian; Volume 8: EMI Control Methodology and Procedures, by MichelMardiguian; and in Chapter 8: Electromagnetic Compatibility forElectrical Engineering, by B. A. Austin, of Electrical Engineer'sReference Book, by G. R. Jones, M. A. Laughton, and M. G. Say(Butterworth-Heinemann, Oxford, UK, 1993). Representative devicesinclude instruments, displays (e.g., plasma displays), imaging equipment(e.g., magnetic resonance imaging equipment), computer equipment (e.g.,servers), communications equipment (e.g., cellular phones), medicaldevices and the like. Representative enclosed areas include rooms (e.g.,secure meeting rooms and test equipment facilities), transmissionfacilities (or portions thereof), cabinets, tents and the like.

Preferred embodiments of the EMI shielding films and articles canprovide an optically transparent, flexible or extensible shield that canblock the transmission of unwanted electromagnetic energy out of or intoelectronic equipment and other devices that can cause or are sensitiveto electromagnetic interference. These preferred EMI shielding films andarticles can provide dramatically better mechanical durability andcorrosion resistance than typical commercially available opticallytransparent EMI shielding films, while providing comparable opticaltransparency and shielding power. Surprisingly, these preferred EMIshielding films retain their EMI shielding capability even whenstretched, bent, or creased. The EMI shielding films preferably retaintheir EMI shielding capability when strained in a tensile mode by 5%,10%, or more of their original length. More preferably, they retaintheir EMI shielding capability when strained in a tensile mode by 20%,30%, 40% or even 50% or more of their original length. This is anunexpected result, since commercially available EMI shielding films losetheir EMI shielding capability at strains well below 10% and even 5%,e.g., at 2% strain. The EMI shielding films preferably retain their EMIshielding capability when bent at a 45° angle, and more preferably whenbent at a 90° angle. Most preferably, they retain their EMI shieldingcapability when bent or creased at a 180° angle. This is an unexpectedresult, since commercially available EMI shielding films lose their EMIshielding capability when bent or even when roughly handled.

The following tests were used to evaluate various EMI shielding films:

Corrosion Test

Two strips 25.4 mm wide by about 254 to 305 mm long were cut from thecenter of a film sample. The strips were placed in jars containing 20%KCl solution at room temperature so that about 150 to 200 mm of eachstrip was immersed into the salt solution. The jar tops were screwedonto the jars to prevent the salt solution from evaporating. The stripswere removed after 15 minutes of immersion, placed support side down ona dry paper towel and wiped with tissue or a paper towel along the widthof the strip. Medium pressure was applied while wiping. The strips werenext washed with cold water to remove salt from the surface and the filmsurface appearance was observed. The appearance rating was based on avisual estimate of the amount of the metal layer removed after wipingthe strip, expressed as a percentage of the original metal layer area.

Corrosion Under Electrical Current Test

Two strips 25.4 mm wide by 203 mm long were cut from the center of afilm sample. The narrow ends of the strips were painted on both sideswith No. 22-201 silver paint (Katy Company). After the silver paintdried, copper was folded over the painted edges to form a durableelectrode at each end of the strip. Alligator clips were used to connecta power supply to the copper electrodes. A voltage of 4.0 volts wasapplied between the contacts and the resulting current was measured andrecorded. A 125 to 150 mm long section near the center of each strip wasthen submerged into 20% KCl solution at room temperature. The electricalcurrent was measured and recorded during the course of the immersiontime.

Adhesion Test

Squares about 254 mm wide by about 254 mm long were cut from the centerof a film sample. 25.4 mm wide by 178 mm long pieces of masking tape andfilament tape were each applied to the film in both the MD and TDdirections, pressed with a 2.3 kg roller, then aged for one week. Theadhesion test rating was based on a visual estimate of the amount of themetal layer remaining after peeling away the tapes, expressed as apercentage of the original metal layer area.

Conductivity vs. Strain Test

As an approximate measure of the level of strain at which an EMIshielding film would lose its EMI shielding capability, EMI shieldingfilm samples were stretched using a SINTECH™ 200/S TENSILE TESTER(Instron Corp.) to determine the percent strain at which the film wouldstop conducting electricity. A strip prepared as in the Corrosion UnderElectrical Current test was clamped into the jaws of the tensile tester,and alligator clips were used to connect a power supply to the copperelectrodes. While using a gauge length of 101.6 mm and a crosshead speedof 25.4 mm/min, a constant voltage of 4 volts was supplied to the stripand the current flow was measured and recorded vs. % strain.

Sheet Resistance Test

The EMI shielding films were evaluated for sheet resistance, or surfaceresistivity, using a non-contact conductivity measuring device (Model717B Benchtop Conductance Monitor, Delcom Instruments Inc.).

Solar Heat Gain Coefficient and Shading Coefficient

The value Te is defined as the ratio, expressed in percent, of the solarenergy transmitted by a specimen from 250 nm to 2500 nm divided by thetotal incident solar energy. The value Ae is defined as the ratio,expressed in percent, of the solar energy absorbed by a specimen from250 nm to 2500 nm divided by the total incident solar energy. Solarproperties are calculated using solar irradiance data from ASTM E891using air mass 1.5. The Solar Heat Gain Coefficient (SHGC) is calculatedasSHGC=Te+0.27(Ae).The Shading Coefficient (SC) is defined as the ratio of the Solar HeatGain Coefficient through a given glazing to that through a single paneof standard 3.2 mm thick window glass, and is calculated asSC=SHGC/87.0.

EMI Shielding Strength

EMI Shielding Strength was evaluated according to ASTM D-4935-99, via afar field type test using a coaxial TEM cell. The results are reportedin decibels (dB).

The EMI shielding films and articles will now be described withreference to the following non-limiting examples, in which all parts andpercentages are by weight unless otherwise indicated.

EXAMPLE 1

(Layer 1) An approximately 300 meter long roll of 0.05 mm thick by 508mm wide PET support (MELINEX™ No. 453 film, DuPont Teijin Films) wasloaded into a roll to roll vacuum chamber like that shown in FIG. 6A.The pressure in the vacuum chamber was reduced to 3×10⁻⁴ torr. Thesupport was sequentially plasma pretreated and acrylate coated duringone pass at a web speed of 36.6 m/min. The plasma pretreatment utilizeda chrome target and an unbalanced dc magnetron operated at 1500 wattspower (429 volts and 3.5 amps) under a nitrogen atmosphere with anitrogen gas flow of 70 sccm. The acrylate coating employed a 50:50mixture of IRR214 acrylate (UCB Chemicals) and lauryl acrylate that hadbeen degassed for 1 hour by placing a container of the liquid monomermixture into a bell jar and reducing pressure to approximately 1millitorr. The degassed monomer was pumped at a flow rate of 2.35 ml/minthrough an ultrasonic atomizer into a vaporization chamber maintained at274° C. Using a drum temperature of −18° C., the monomer vapor wascondensed onto the moving web and electron beam crosslinked using asingle filament gun operated at 7.59 kV and 2.0 milliamps.

(Layer 2) The web direction was reversed. Again operating at 36.6 m/min,the acrylate surface was plasma treated and coated with magnetronsputtered silver. The plasma pretreatment was as before but at 413 voltsand 3.64 amps. The silver was sputtered at 10,000 watts power (590 voltsand 16.96 amps), a drum temperature of 25° C. and an argon atmospherewith an argon gas flow of 90 sccm.

(Layer 3) The web direction was again reversed. Again operating at 36.6m/min, a crosslinked spacing layer was formed using the monomer mixturedescribed above, but without plasma pretreatment of the silver surfaceprior to monomer deposition. Using a drum temperature of −17° C. and theother monomer deposition conditions described above, the monomer vaporwas condensed onto the moving web and electron beam crosslinked using asingle filament gun operated at 7.8 kV and 3.8 milliamps.

(Layer 4) The web direction was again reversed. Again operating at 36.6m/min, the crosslinked spacing layer was plasma pretreated and coatedwith magnetron sputtered silver. The plasma pretreatment was as beforebut using 429 volts and 3.5 amps. The silver was sputtered as before butat 590 volts, 16.94 amps, and a drum temperature of 22° C.

(Layer 5) The web direction was again reversed. A protective layer wasformed using the monomer mixture described above, but without plasmapretreatment of the silver surface prior to monomer deposition. Using adrum temperature of −17° C. and the other monomer deposition conditionsdescribed above, the monomer vapor was condensed onto the moving web andelectron beam crosslinked using a single filament gun operated at 10.11kV and 3.8 milliamps.

The optical properties of the resulting five layer infrared-rejectingacrylate/Ag/acrylate/Ag/acrylate optical stack are shown in FIG. 7.Curves T and R respectively show the transmission (T_(vis)) andreflection for the finished film. Using optical modeling and assuming aBruggerman density for silver of 0.97, the five layers had calculatedthicknesses of 120 nm (acrylate layer 1)/12 nm (Ag layer 2)/85 nm(acrylate layer 3)/12 nm (Ag layer 4)/120 nm (acrylate layer 5).

EXAMPLE 2

Using the method of Example 1, a PET support was covered with a fivelayer acrylate/Ag/acrylate/Ag/acrylate optical stack, but using plasmapretreatment on both the top and bottom of the metal layers. Theindividual layer differences were as follows:

(Layer 1) The support plasma pretreatment was as before but at 1000watts power (402 volts and 2.5 amps) and a nitrogen gas flow of 102sccm. The monomer flow rate was 2.45 ml/min and the vaporization chambertemperature was 276° C. The monomer vapor was condensed onto the movingweb using a −21° C. drum temperature. The electron beam filament wasoperated at 8.0 kV and 6.5 milliamps.

(Layer 2) The plasma pretreatment was at 1000 watts power (309 volts and3.34 amps) and a nitrogen gas flow of 90 sccm. The silver was sputteredat 570 volts and 17.88 amps, a drum temperature of 21° C. and an argongas flow of 93.2 sccm.

(Layer 3) The silver surface was plasma pretreated prior to depositionof the spacing layer. The plasma pretreatment utilized a chrome targetand 1000 watts power (308 volts and 3.33 amps). Using a drum temperatureof −23° C., the monomer vapor was condensed onto the moving web andelectron beam crosslinked using a single filament gun operated at 8.0 kVand 6.0 milliamps.

(Layer 4) The plasma pretreatment was at 316 volts and 3.22 amps, andthe nitrogen gas flow rate was 90 sccm. The silver was sputtered at 567volts and 17.66 amps, a drum temperature of 20° C., and an argon gasflow of 95.5 sccm.

(Layer 5) The silver surface was plasma pretreated prior to depositionof the protective layer. The plasma pretreatment was the same as inLayer 3. Using a drum temperature of −23° C., the monomer vapor wascondensed onto the moving web and electron beam crosslinked using asingle filament gun operated at 8.0 kV and 6.2 milliamps.

The optical properties of the resulting five layer infrared-rejectingacrylate/Ag/acrylate/Ag/acrylate optical stack are shown in FIG. 8.Curves T and R respectively show the transmission and reflection for thefinished film. Using optical modeling and assuming a Bruggerman densityfor silver of 0.97, the five layers had calculated thicknesses of 120 nm(acrylate layer 1)/9 nm (Ag layer 2)/95 nm (acrylate layer 3)/9 nm (Aglayer 4)/120 nm (acrylate layer 5).

EXAMPLES 3-5

Using the method of Example 2, five layer infrared-rejectingacrylate/Ag/acrylate/Ag/acrylate optical stacks with silver layers ofvarying thickness were formed on a PET support. The resulting films wereevaluated for appearance, transmission (T_(vis)), reflection, solar heatgain coefficient (SHGC), shading coefficient (SC) and sheet resistivity.The processing conditions and evaluation results are set out below inTable 1.

TABLE 1 Ex. 3 Ex. 4 Ex. 5 Layer 1 Deposited material Monomers MonomersMonomers Line speed (m/min) 36.6 36.6 36.6 Plasma (Watts) 1000 1000 1000Drum temp (° C.) −21 −21 −21 Monomer feed (ml/min) 2.65 2.65 2.65 Layer2 Deposited material Ag Ag Ag Line speed (m/min) 35.1 36.6 38.1 Plasma(Watts) 1000 1000 1000 Drum temp (° C.) 26 26 26 Sputter power (kW) 1010 10 Layer 3 Deposited material Monomers Monomers Monomers Line speed(m/min) 36.6 36.6 36.6 Plasma (Watts) 1000 1000 1000 Drum temp (° C.)−19 −19 −19 Monomer feed (ml/min) 2.65 2.65 2.65 Layer 4 Depositedmaterial Ag Ag Ag Line speed (m/min) 35.1 36.6 38.1 Plasma (Watts) 10001000 1000 Drum temp (° C.) 28 28 28 Sputter power (kW) 10 10 10 Layer 5Deposited material Monomers Monomers Monomers Line speed (m/min) 36.636.6 36.6 Plasma (Watts) 1000 1000 1000 Drum temp (° C.) −18 −18 −18Monomer feed (ml/min) 1.35 1.35 1.35 Results: Appearance Good Good GoodTrans-Luminous Y (T_(vis)) 72.37 72.14 71.53 Refl-Luminous Y 12.36 10.9211.18 SHGC 46.28 46.84 48.04 SC 0.5320 0.5384 0.5522 Sheet Resistivity3.929 4.505 4.673 (Ohms/Square)

The results in Table 1 show the use of varying line speeds to alter thethickness of the metal layers. Films having a T_(vis) as high as 72% andsheet resistance as low as 3.9 Ohms/square were obtained. Two sampleseach of the films of Examples 4 and 5 were also evaluated using theconductivity vs. strain test. The results are shown in FIG. 9 and FIG.10, respectively. All film samples conducted current at up to 50% ormore strain.

Comparative Example 1

A commercial product based on transparent silver layers and an indiumoxide inorganic dielectric (XIR™ 75 film, Southwall Technologies Inc.)was evaluated using the conductivity vs. strain test. The sample failedwhen subjected to only 1% strain.

EXAMPLES 6-11

Using the method of Examples 3 through 5, five layer infrared-rejectingacrylate/Ag/acrylate/Ag/acrylate optical stacks were formed on a PETsupport (Examples 6-9) or a birefringent multilayer optical film support(3M™ Solar Reflecting Film No. 41-4400-0146-3, Examples 10-11) andoptionally given a plasma post-treatment. The thickness of Layer 5 wasvaried by altering the deposition conditions as shown below. Theresulting films were evaluated for appearance, transmission, reflection,solar heat gain coefficient, shading coefficient and sheet resistivity.The processing conditions and evaluation results are set out below inTable 2.

TABLE 2 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Support PET PET PET PETMOF MOF Layer 1 Deposited material Monomers Monomers Monomers MonomersMonomers Monomers Line speed (m/min) 36.6 36.6 36.6 36.6 36.6 36.6Plasma (Watts) 1000 1000 1000 1000 1000 1000 Drum temp (° C.) −21 −21−21 −21 −21 −21 Monomer feed (ml/min) 2.65 2.65 2.65 2.65 2.65 2.65Layer 2 Deposited material Ag Ag Ag Ag Ag Ag Line speed (m/min) 36.636.6 36.6 36.6 36.6 36.6 Plasma (Watts) 1000 1000 1000 1000 1000 1000Drum temp (° C.) 26 26 26 26 19 19 Sputter power (kW) 10 10 10 10 10 10Layer 3 Deposited material Monomers Monomers Monomers Monomers MonomersMonomers Line speed (m/min) 36.6 36.6 36.6 36.6 36.6 36.6 Plasma (Watts)1000 1000 1000 1000 1000 1000 Drum temp (° C.) −19 −19 −19 −19 −20 −20Monomer feed (ml/min) 2.65 2.65 2.65 2.65 2.85 2.85 Layer 4 Depositedmaterial Ag Ag Ag Ag Ag Ag Line speed (m/min) 36.6 36.6 36.6 36.6 36.636.6 Plasma (Watts) 1000 1000 1000 1000 1000 1000 Drum temp (° C.) 28 2828 28 23 23 Sputter power (kW) 10 10 10 10 10 10 Layer 5 Depositedmaterial Monomers Monomers Monomers Monomers Monomers Monomers Linespeed (m/min) 36.6 36.6 36.6 36.6 36.6 36.6 Plasma (Watts) 1000 10001000 1000 1000 1000 Drum temp (° C.) −18 −18 −18 −18 −17 −17 Monomerfeed (ml/min) 1.45 1.25 1.35 1.35 1.35 1.35 Plasma Post- Treatment Linespeed (m/min) 36.6 36.6 36.6 Plasma (Watts) 1500 1000 1000 Results:Appearance Good Good Good Good Good Good Trans-Luminous Y 71.51 70.0968.19 72.59 72.69 72.51 (T_(vis)) Refl-Luminous Y 11.73 12.02 11.86 7.7511.16 10.15 SHGC 46.60 46.25 44.82 46.81 44.97 45.63 SC 0.5356 0.53160.5152 0.5381 0.5169 0.5244 Sheet Resistivity 4.23 4.38 5.709 5.2083.927 4.389 (Ohms/Square)

The results in Table 2 show the use of two different substrates, varyingprotective topcoat thickness and an optional plasma post-treatment ofthe topcoat. Films having a T_(vis) as high as about 73% and sheetresistance as low as 3.9 Ohms/square were obtained. Two samples of thefilm of Example 11 were also evaluated using the conductivity vs. straintest. The results are shown in FIG. 11. Both film samples conductedcurrent at up to 50% or more strain.

EXAMPLE 12

Using the method of Example 2, a PET support was covered with a fivelayer acrylate/Ag/acrylate/Ag/acrylate optical stack, but using plasmapretreatment on both the top and bottom of the metal layers. Theindividual layer differences were as follows:

(Layer 1) The support plasma pretreatment was at 1000 watts power butusing 322 volts, 3.15 amps and a nitrogen gas flow of 70 sccm. Themonomer flow rate was 2.65 ml/min and the vaporization chambertemperature was 274° C. The monomer vapor was condensed onto the movingweb using a −20° C. drum temperature. The electron beam filament wasoperated at 8.04 kV and 5.7 milliamps.

(Layer 2) The plasma pretreatment was at 1000 watts power but using 378volts, 3.09 amps and a nitrogen gas flow of 70 sccm. The silver wassputtered at 547 volts, 18.36 amps, a drum temperature of 26° C. and anargon gas flow of 70 sccm.

(Layer 3) The plasma pretreatment was at 1000 watts power but using 327volts and 3.1 amps. The monomer vapor was condensed onto the moving webusing a drum temperature of −19° C. The electron beam filament wasoperated at 8.04 kV and 6.3 milliamps.

(Layer 4) The plasma pretreatment was at 1000 watts power but using 328volts, 3.07 amps and a nitrogen gas flow rate of 70 sccm. The silver wassputtered at 546 volts, 18.34 amps, a drum temperature of 28° C., and anargon gas flow of 70 sccm.

(Layer 5) The plasma pretreatment was at 1000 watts power but using 359volts and 2.82 amps. The monomer vapor was condensed onto the moving webusing a drum temperature of −18° C. The electron beam filament wasoperated at 8.04 kV and 4.6 milliamps.

The optical properties of the resulting five layer infrared-rejectingacrylate/Ag/acrylate/Ag/acrylate optical stack are shown in FIG. 12.Curves T and R respectively show the transmission and reflection for thefinished film. The film had a T_(vis) of 71.5%. The film was next cutinto a 30.5 cm by 2.54 cm strip. The edges were painted with a silverconductive paint (SILVER PRINT™, O.K. Thorsen Inc.). A 2.54 cm by 2.54cm copper foil was folded over each of the opposing narrow ends of thestrip and connected using test leads equipped with alligator clips to a0-20 volt power supply (Model 6253A dual DC, Hewlett Packard, Inc.). Avoltage was applied to the strip, and the current and strip temperaturewere measured as a function of time. When the strip temperature stoppedincreasing, a higher voltage was applied. The results are shown below inTable 3.

TABLE 3 Power Time (min) Volts Amps Power (W) (W/cm²) Temp (° C.) 0 0 0— — 23.4 1 16 0.265 4.24 0.0548 51.3 2 16 0.265 4.24 0.0548 54 3 160.265 4.24 0.0548 55.4 4 16 0.265 4.24 0.0548 56.4 6 16 0.265 4.240.0548 57.8 10 16 0.265 4.24 0.0548 58.8 11 20 0.34 6.8 0.0878 69.9 1220 0.34 6.8 0.0878 73.1 15 20 0.34 6.8 0.0878 75.6 17 20 0.34 6.8 0.087876.4 19 20 0.34 6.8 0.0878 76.3 21 24 0.42 10.08 0.1302 103.1 22 24 0.4210.08 0.1302 99.8 23 24 0.42 10.08 0.1302 103.5 25 24 0.42 10.08 0.1302105.4 29 24 0.42 10.08 0.1302 106.9 33 24 0.42 10.08 0.1302 107.4 34 240.42 10.08 0.1302 107.4

The results in Table 3 show that the film could withstand very highpower densities and very high temperatures without circuit failure. Thestrip was allowed to cool and then 16 volts were applied to the strip,resulting in a measured current of 0.27 amps. The film became warm tothe touch. The film was next bent over the edge of a counter top at a45° angle, and then at a 90° angle. The film still felt warm to thetouch and the current remained at 0.27 amps. The film was next bent at a180° angle. The sample still felt warm to the touch and the currentremained at 0.27 amps. Had cracking occurred, hot spots would havearisen in the film and a substantial current change (or a completecessation of current flow) would have been observed, accompanied by aloss in EMI shielding capability.

Comparative Example 2

Using the method of Example 12, a sample of XIR 75 indium oxide film(Southwall Technologies Inc.) was powered and heated. The sample failedwhen subjected to 24 volts or when bent. The results are set out belowin Table 4.

TABLE 4 Power Time (min) Volts Amps Power (W) (W/cm²) Temp (° C.) 0 80.122 0.976 0.0130 23.1 2 8 0.122 0.976 0.0130 32.3 4 8 0.122 0.9760.0130 33 6 8 0.122 0.976 0.0130 33.4 7 8 0.122 0.976 0.0130 33.6 8 80.122 0.976 0.0130 33.4 10 12 0.182 2.184 0.0291 41.7 11 12 0.182 2.1840.0291 42.5 12 12 0.182 2.184 0.0291 43 13 12 0.182 2.184 0.0291 43.1 1412 0.182 2.184 0.0291 43.5 15 12 0.182 2.184 0.0291 43.6 16 12 0.1822.184 0.0291 43.6 17 12 0.182 2.184 0.0291 43.7 18 12 0.182 2.184 0.029143.7 20 16 0.24 3.84 0.0512 53.3 22.5 16 0.24 3.84 0.0512 55.1 25 160.24 3.84 0.0512 55.7 26 16 0.24 3.84 0.0512 55.7 27 16 0.24 3.84 0.051255.5 28 16 0.24 3.84 0.0512 55.7 30 20 0.29 5.8 0.0773 67.3 32 20 0.295.8 0.0773 71.2 34 20 0.29 5.8 0.0773 72 37.5 20 0.29 5.8 0.0773 72.3 3820 0.29 5.8 0.0773 72.8 39 20 0.29 5.8 0.0773 72.7 40 20 0.29 5.8 0.077372.7 41 24 0 (Failed) (Failed) —

The results in Table 4 show that the comparison film could beelectrically heated. However, when the voltage was increased to 24 voltsthe film failed. This was believed to be due to cracking of the indiumoxide layer. A separate sample of the comparison film was electricallyheated using an applied voltage of 16 volts, resulting in a measuredcurrent of 0.235 amps. The comparison film became warm to the touch.When the comparison film was bent over the edge of a counter top at a45° angle, the film failed. Using optical microscopy, a crack could beobserved in the coating.

EXAMPLE 13

A 304 mm by 304 mm sample of the film of Example 5 having a sheetresistance of 4.2 ohms/square was electrically joined to busbars so thatboth metal layers could be grounded.

EXAMPLE 14

A PET support was covered with a three layer acrylate/Ag/acrylate stack.The individual layers were formed as follows:

(Layer 1) A 914 meter long roll of 0.05 mm thick×508 mm wide PET film(MELINEX™ No. 453 film, DuPont-Teijin Films) was loaded into a roll toroll vacuum chamber, and the chamber pressure was pumped to a pressureof 8×10-6 torr. The PET film was coated with an acrylate mixturecontaining 48.5% IRR214 acrylate, 48.5% lauryl acrylate, and 3.0%EBECRYL™ 170 adhesion promoter. The acrylate mixture was vacuum degassedprior to coating, and pumped at a flow rate of 2.35 ml/min. through anultrasonic atomizer into a vaporization chamber maintained at 275° C.The PET film was passed over a coating drum maintained at 0° C. at a webspeed of 30.4 meters/min, where the monomer vapor was condensed, andthen electron beam crosslinked with a single filament operated at 8.0 kVand 2.0 milliamps. This produced an acrylate layer having a 100 nmthickness after cure.

(Layer 2) The web direction was reversed inside the chamber, and theacrylate surface was sputter coated with a silver layer. The silver wassputtered at 10 kW power, using argon as the sputtering gas at a chamberpressure of 2.0 millitorr, and a web speed of 30.4 meters/minute toprovide a 10 nm thick silver layer.

(Layer 3) The web direction was again reversed. Using the sameconditions as for Layer 1, a 100 nm thick acrylate layer was depositedonto the silver layer.

The resulting three layer film stack exhibited good spectraltransmission and reflectance characteristics (i.e., was lighttransmissive), and had an electrical resistivity of 10 ohms/sq. When theCorrosion Under Electrical Current Test was performed the current fellto zero a few seconds after immersion. This indicated that silvercorrosion, electrical circuit failure and likely loss of EMI shieldingcapability had taken place more rapidly than would be desirable undersevere corrosion conditions.

EXAMPLE 15

A second three layer film stack was prepared in the same manner asExample 14, but using a nitrogen plasma pretreatment of the PET, Layer 1acrylate coating and Layer 2 silver coating prior to the deposition ofthe subsequent layer. The resulting film was light transmissive. Thenitrogen plasma was applied using an unbalanced dc magnetron source,operated at 1.0 kW and 2.0 millitorr pressure. When the Corrosion UnderElectrical Current Test was performed the current did not fall to zerountil 500 to 600 seconds after immersion, indicating much slower silvercorrosion and electrical circuit failure than in Example 14, andimproved retention of EMI shielding capability.

EXAMPLE 16

A three layer film stack was prepared in the same manner as Example 14,with the addition of 2% ethylene glycol bis-thioglycolate to the monomermixture. The resulting film was light transmissive. When the CorrosionUnder Electrical Current Test was performed the current fell to zero 500to 600 seconds after immersion, indicating slower silver corrosion andelectrical circuit failure than in Example 14, and comparableperformance to Example 15.

EXAMPLE 17

A three layer film stack was prepared in the same manner as Example 14,but using nitrogen plasma pretreatment as in Example 15 and a 2%ethylene glycol bis-thioglycolate addition as in Example 16. Theresulting film was light transmissive. When the Corrosion UnderElectrical Current Test was performed the current remained constant forover 900 seconds after immersion, at which time the test was terminated.This indicated that silver corrosion and the likelihood of circuitfailure and loss of EMI shielding capability had been further reduced incomparison to Examples 14 to 16.

EXAMPLE 18

The film of Example 12 was tested for optical transmission at 550 nm,Sheet Resistance and EMI Shielding Strength. The measured opticaltransmission was 75%, the surface resistivity was 4.5 Ohm/sq, and theEMI shielding strength was 29 dB.

Comparative Example 3

Using the method of Example 18, a sample of AgHT™-4 opticallytransparent EMI shielding film (CP Films) was evaluated. The measuredoptical transmission was 76%, the surface resistivity was 4.7 Ohm/sq,and the EMI shielding strength was 29 dB. The film was crinkled by handand retested for EMI Shielding Strength. The EMI shielding strengthdecreased to 5 dB. A fresh sample of the film was also evaluated forcorrosion and strain resistance. Circuit failure occurred in 20 secondsin the Corrosion Under Electrical Current Test, and conductivity fell tozero at 2% strain in the Conductivity vs. Strain Test.

EXAMPLE 19

Using the method of Example 12, a PET support was covered with a fivelayer acrylate/Ag/acrylate/Ag/acrylate optical stack using plasmapretreatment on both the top and bottom of the metal layers. The monomermixture contained 2% ethylene glycol bis-thioglycolate. The otherindividual layer differences were as follows:

(Layer 1) The support plasma pretreatment was at 1000 watts power butusing 428 volts and 2.3 amps. The monomer vapor was condensed onto themoving web using a −17° C. drum temperature. The electron beam filamentwas operated at 8.0 kV and 2.8 milliamps.

(Layer 2) The plasma pretreatment was at 1000 watts power but using 368volts and 2.72 amps. The silver was sputtered at 632 volts, 15.8 amps, adrum temperature of 31° C. and an argon gas flow of 87 sccm.

(Layer 3) The plasma pretreatment was at 1000 watts power but using 430volts and 2.3 amps. The monomer vapor was condensed onto the moving webusing a drum temperature of −17° C. The electron beam filament wasoperated at 8.0 kV and 4.8 milliamps.

(Layer 4) The plasma pretreatment was at 1000 watts power but using 368volts and 2.72 amps. The silver was sputtered at 634 volts, 15.8 amps, adrum temperature of 32° C., and an argon gas flow of 87 sccm.

(Layer 5) The plasma pretreatment was at 1000 watts power but using 448volts and 2.2 amps. The monomer vapor was condensed onto the moving webusing a drum temperature of −19° C. The electron beam filament wasoperated at 8.0 kV and 5.7 milliamps.

The measured optical transmission of the resulting film was 70%, thesurface resistivity was 5.6 Ohm/sq, and the EMI Shielding Strength was28 dB. The film was crinkled by hand as in Comparative Example 3 andretested for EMI Shielding Strength. The EMI Shielding Strength remainedat 28 dB, indicating full retention of EMI shielding ability.

EXAMPLE 20

Using the general method of Example 1 (but employing chromium sputteringin place of plasma pretreatment in order to deposit a layer of chromiummetal), a PET support was covered with a seven layeracrylate/Cr/Ag/acrylate/Cr/Ag/acrylate optical stack. The monomermixture contained a 43:43:14 mixture of IRR214 acrylate, lauryl acrylateand DAROCUR™ 1173 photoinitiator (Ciba Specialty Chemicals). Thephotoinitiator was added to the monomer mixture after vacuum degassingand just prior to coating. The individual layers were formed as follows:

(Layer 1) The pressure in the vacuum chamber was reduced to 2×10⁻⁵ torr.The support was sequentially plasma pretreated and acrylate coated inone pass at a 24.4 m/min web speed, using a 500 sccm nitrogen gas flow,RF plasma power of 800 watts at 450 kHz, and a −9.4° C. coating drumtemperature. The three component monomer mixture was pumped at a 1.5ml/min flow rate. UV lamps were employed to cure the monomer mixture.

(Layer 2) The web direction was reversed. The acrylate layer was coatedwith chromium at 12.2 m/min using 2.5 kW DC sputtering power and a 10sccm argon gas flow.

(Layer 3) The web direction was reversed. The chromium layer was coatedwith silver at 24.4 m/min using 9.0 kW DC sputtering power and a 10 sccmargon gas flow.

(Layer 4) Sequentially in the same pass, the silver layer was coatedwith the monomer mixture as in Layer 1.

(Layer 5) The web direction was reversed. The acrylate layer was coatedwith chromium as in Layer 3.

(Layer 6) The web direction was reversed. Operating at 24.4 m/min, thechromium layer was coated with silver as in Layer 4.

(Layer 7) Sequentially in the same pass, the silver layer was coatedwith the monomer mixture as in Layer 1.

The optical properties of the resulting seven layer infrared-rejectingacrylate/Cr/Ag/acrylate/Cr/Ag/acrylate optical stack are shown in FIG.13. Curves T and R respectively show the transmission and reflection forthe finished film. The finished film possessed a visible transmission of76%, haze of 0.68%, surface resistivity of 5.9 Ohms/sq and EMI shieldingstrength of 33 dB at 5 GHz.

EXAMPLE 21

Using the general method of Example 20, a PET support was covered with asix layer Ti/Ag/acrylate/Ti/Ag/acrylate optical stack. The monomermixture contained a 64:28:8 mixture of IRR214 acrylate, lauryl acrylate,and ethylene glycol bis-thioglycolate. The individual layers were formedas follows:

(Layer 1) The support as supplied by the manufacturer includes anunidentified treatment on one side. The untreated side of the supportwas coated with titanium at 36.6 m/min using a −23° C. drum temperature,2.8 kW DC sputtering power (426 volts and 6.8 amps) and a 50 sccm argongas flow.

(Layer 2) Sequentially in the same pass, the titanium layer was coatedwith silver using a −23° C. drum temperature, 15 kW DC sputtering power(779 volts and 19.6 amps) and a 150 sccm argon gas flow.

(Layer 3) Sequentially, in the same pass, the silver layer was coatedwith the monomer mixture using a flow rate of 2.4 ml/min, a 274° C.vaporization chamber temperature, a −23° C. drum temperature and asingle filament electron beam gun operated at 7.5 kV and 9.7 milliamps.

(Layer 4) The web direction was reversed. The acrylate layer was coatedwith titanium at 36.6 m/min using a −16° C. drum temperature, 2.8 kW DC(412 volts and 11.1 amps) sputtering power and a 90 sccm argon gas flow.

(Layer 5) Sequentially in the same pass, the titanium layer was coatedwith silver using a −16° C. drum temperature, 15 kW DC sputtering power(778 volts and 19.5 amps) and a 150 sccm argon gas flow.

(Layer 6) Sequentially in the same pass, the silver layer was coatedwith the monomer mixture as in Layer 3 using a −17° C. drum temperatureand a single filament electron beam gun operated at 7.5 kV and 7.2milliamps.

The optical properties of the resulting six layer infrared-rejectingTi/Ag/acrylate/Ti/Ag/acrylate optical stack are shown in FIG. 14. CurvesT and R respectively show the transmission and reflection for thefinished film. The finished film possessed a visible transmission of73%, haze of 0.44% and surface resistivity of 6.2 Ohms/sq.

EXAMPLE 22

Using the general method of Example 21, a PET support was covered with asix layer Ti/Ag/acrylate/Ti/Ag/acrylate optical stack. The individuallayers were formed as follows:

(Layer 1) The pressure in the vacuum chamber was reduced to 1.5×10⁻⁴torr. The web was coated with titanium at 24.4 m/min using a −17° C.drum temperature, 2.8 kW DC sputtering power (404 volts and 7.2 amps)and a 10 sccm argon gas flow.

(Layer 2) Sequentially in the same pass, the titanium layer was coatedwith silver using a −17° C. drum temperature, 15 kW DC sputtering power(742 volts and 20.5 amps) and a 90 sccm argon gas flow.

(Layer 3) Sequentially in the same pass, the silver layer was coatedwith the monomer mixture using a flow rate of 1.8 ml/min, a 274° C.vaporization chamber temperature, a −18° C. drum temperature and asingle filament electron beam gun operated at 7.5 kV and 10.9 milliamps.

(Layer 4) The web direction was reversed. The acrylate layer was coatedwith titanium at 24.4 m/min using a −16° C. drum temperature, 2.8 kW DC(371 volts and 7.8 amps) sputtering power and a 10 sccm argon gas flow.

(Layer 5) Sequentially in the same pass, the titanium layer was coatedwith silver using a −16° C. drum temperature, 15 kW DC sputtering power(739 volts and 20.6 amps) and a 90 sccm argon gas flow.

(Layer 6) The web direction was reversed. The silver layer was coatedwith the monomer mixture as in Layer 3 and at 45.7 m/min using a flowrate of 1.5 ml/min, an −18° C. drum temperature and a single filamentelectron beam gun operated at 7.5 kV and 4.1 milliamps.

The optical properties of the resulting six layer infrared-rejectingTi/Ag/acrylate/Ti/Ag/acrylate optical stack are shown in FIG. 15. CurvesT and R respectively show the transmission and reflection for thefinished film. The finished film exhibited visible transmission of 78%,haze of 0.76%, surface resistivity of 6.5 Ohms/sq and EMI shieldingstrength of 32 dB at 5 GHz.

EXAMPLE 23

The film of Example 20 was thermoformed so that a portion of the filmhad a three-dimensional semispherical indentation. The thermoformingprocess was carried out by taping the film over a 45 mm diameter hole ina plastic slab. Vacuum was pulled on the film through the hole in theslab while heating the film using a heat gun until the film was hotenough to deform downward into the hole. The heat gun was removed andthe film was permitted to cool and removed from the slab. The resultingthermoformed semispherical indentation had a 5 mm depth with respect tothe nominally planar region of the remaining film. The indentationpersisted when the film was held by hand at two opposing ends and pulledsufficiently taut to remove apparent slackness. The deformed region waslight transmissive and exhibited a surface resistivity of 5.5 Ohms/sqand haze of 1.6% compared to values of 5.9 Ohms/sq and 0.68%, for thenon-thermoformed film.

Comparative Example 4

Using the method of Example 23, XIR 75 indium oxide film wasthermoformed so that a portion of the film had a three-dimensionalsemispherical indentation. The surface resistivity of the thermoformedregion increased to 5,000 Ohms/sq compared to 5.2 Ohms/sq for thenon-thermoformed film. The large surface resistivity for thethermoformed film is consistent with loss of one or more of electricalconductivity, infrared reflectivity and EMI shielding strength. The hazeof the thermoformed region increased to 13.9% compared to 0.56% for thenon-thermoformed film.

Comparative Examples 5-8

Using the method of Example 23, several commercially available filmsfrom CPFilms, Inc. were thermoformed so that a portion of each film hada three-dimensional semispherical indentation. The films werecharacterized for surface resistivity. The results are shown below inTable 5.

TABLE 5 Comp. Comp. Comp. Comp. Ex. 5 Ex. 6 Ex. 7 Ex. 8 Film AgHT-4AgHT-8 OC-50 ARAL70 Surface Resistivity 3.4 8.4 52 20 (beforethermoforming, Ohms/sq) Surface Resistivity 413 316 719 585 (afterthermoforming, Ohms/sq)

The above results show that the commercial films exhibited significantincreases in surface resistivity (consistent with loss of one or more ofelectrical conductivity, infrared reflectivity and EMI shieldingstrength) when an attempt was made to thermoform them.

EXAMPLE 24

The film of Example 21 was laminated to a 0.25 mm thick supplementalpolycarbonate support (LEXAN™ 8010, General Electric) using No. 467MPtransfer adhesive (3M). The resulting laminated construction was placedin a convection oven at 125° C. for about 20 min to allow the adhesiveto dry. The laminated construction was subsequently thermoformed into athree-dimensional shape corresponding to the front face of a cell phone.The thermoforming process employed a Labform Pressure Former (Hydro-TrimCorporation) operated with a 90 second preheat at about 222° C.,followed by a 90 second thermoforming step at the same temperature. Theresulting thermoformed part was transparent, relatively rigid andself-supporting, with permanently deformed compound curved features. Thesurface resistivity of the resulting thermoformed part was 6.0 Ohms/sqwhich is very similar to the 6.2 Ohms/sq surface resistivity for thenon-thermoformed film.

The thermoformed part is illustrated in FIG. 16. Cell phone cover 300has a face portion 302 with a generally convex shape as viewed from thefront. Indentation 304 designates the microphone location. Indentations306 designate the keypad button locations. Region 308 designates thedisplay area Molding flange 310 surrounds face portion 302, and can beremoved from the finished phone cover using techniques that will befamiliar to those in the art of making molded plastic objects.

Comparative Example 9

Using the method of Example 24, XIR 75 indium oxide film was laminatedto a 0.25 mm thick polycarbonate supplemental support and thermoformed.The resulting thermoformed part was transparent. The surface resistivityof the thermoformed laminated construction containing XIR 75 film was990 Ohms/sq. This is much higher than the 5.2 Ohms/sq surfaceresistivity of the non-thermoformed film.

EXAMPLE 25

The film of Example 21 was laminated between a 0.25 mm thickpolycarbonate supplemental support (Lexan 8010, General Electric) andVIKUITI™ Enhanced Specular Reflector (ESR) multilayer optical film (3M)using No. 467MP transfer adhesive (3M). The resulting laminatedconstruction was dried, then thermoformed into the samethree-dimensional cell phone front face shape using the method ofExample 24. The VIKUITI ESR film surface was placed against the mold.The resulting thermoformed part was not light transmissive and possesseda silver appearance due to the inclusion of the VIKUITI ESR film in theconstruction under the transparent Example 21 film and polycarbonatesupplemental support. The surface resistivity of the resultingthermoformed part was 6.4 Ohms/sq which is very similar to the 6.2Ohms/sq surface resistivity of the non-thermoformed film.

Comparative Example 10

Using the method of Example 25, XIR 75 indium oxide film was laminatedbetween a 0.25 mm, thick polycarbonate supplemental support and VIKUITIESR Film, dried, and thermoformed into the same three-dimensional cellphone front face shape. The resulting thermoformed part possessed asilver appearance due to the inclusion of the VIKUITI ESR film but thesurface resistivity of the thermoformed part was 840 Ohms/sq. This ismuch greater than the 5.2 Ohms/sq surface resistivity of thenon-thermoformed XIR 75 film.

EXAMPLE 26

The film of Example 22 was embossed so that it possessed athree-dimensional pattern. The embossing pattern was produced by feedingthe film of Example 22 at 1.5 m/min through overlapping heated nip rollshaving mating diamond-shaped projections and recesses. The temperatureof the nip rolls was between 176-193° C. The film's surface resistivityactually decreased following embossing, to 3.75 Ohms/sq for the embossedfilm compared to 6.5 Ohms/sq for the unembossed film.

Comparative Example 11

Using the method of Example 26, XIR 75 indium oxide film was embossed ina diamond pattern. The surface resistivity of the XIR 75 film increasedfollowing embossing, to 885 Ohms/sq for the embossed film compared to5.2 Ohms/sq for the unembossed film.

EXAMPLE 27

Using the general method of Examples 1 and 20, a PET support was plasmatreated and covered with a three layer chromium/acrylate/aluminum stack.The individual layers were formed as follows:

(Layer 1) The pressure in the vacuum chamber was reduced to 3×10⁻⁴ torr.The support was plasma pretreated in a separate pass at 15.2 m/min,using a chrome target and an unbalanced dc magnetron operated at 1.5 kWpower (429 volts and 3.5 amps) under a nitrogen atmosphere with anitrogen gas flow of 70 sccm. Chromium was deposited in a second passusing a chrome target and an unbalanced dc magnetron operated at 12 kWpower under an argon atmosphere with an argon gas flow of 91 ml/min anda web speed of 15.2 m/min.

(Layer 2) The monomer mixture of Example 14 was degassed and pumped at aflow rate of 2.79 ml/min through an ultrasonic atomizer into avaporization chamber maintained at 274° C. Using a drum temperature of−18° C., the monomer vapor was is condensed onto the moving web andelectron beam crosslinked using a single filament gun operated at 7.59kV and 2.0 milliamps.

(Layer 3) Aluminum metal was thermally evaporated onto the acrylatelayer to a thickness of 30 nm using resistively heated boats and a webspeed of 50 ft/min.

EXAMPLE 28

An approximately 6 by 12 inch sample of the above film was placed into athermal vacuum forming machine used to make raised graphics forvehicular badging applications. The film was thermoformed into arecessed mold for a three-dimensional graphic spelling the motorcyclename “DUCATI”™. The thermoformed film was backfilled with a polyurethaneresin and cured onto a liner whose backside was coated with a layer ofpressure sensitive adhesive. The result was a non-light transmissive butintensely colored three-dimensional adhesive-backed graphic thatcolor-shifted from magenta to green as the viewing angle changed.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from this invention. Thisinvention should not be restricted to that which has been set forthherein only for illustrative purposes.

1. An electromagnetically shielded article comprising a device orenclosed area that can cause or is sensitive to electromagneticinterference, wherein the device or area is at least partiallysurrounded with a visible light-transmissive film comprising a flexiblesupport, a visible light-transmissive crosslinked polymeric protectivelayer, and an extensible visible light-transmissive metal or metal alloylayer sandwiched therebetween.
 2. An article according to claim 1,wherein the metal or metal alloy layer is substantially continuous, andwherein at least one grounding electrode is connected to the metal ormetal alloy layer.
 3. An article according to claim 1, wherein the metalor metal alloy layer comprises silver and the crosslinked polymericlayer comprises an acrylate polymer.
 4. An article according to claim 1,wherein the film comprises a base coat layer between the support and themetal or metal alloy layer.
 5. An article according to claim 1, whereinthe film comprises two or more additional metal or metal alloy layers.6. An article according to claim 1, wherein an interface between themetal or metal alloy layer and an adjacent layer within the film hasbeen subjected to an adhesion-enhancing treatment, or one or moreadjacent layers within the film comprise an adhesion-enhancing adjuvant,whereby the corrosion resistance of the film is increased.
 7. An articleaccording to claim 2, wherein the grounding electrode comprises a tapecontaining fibers or particles that penetrate the crosslinked polymericlayer.
 8. An article according to claim 1, wherein the film has aperimeter the majority of which is connected to a grounding electrode.9. An article according to claim 1, wherein the film has a perimeter allof which is connected to a grounding electrode.
 10. An article accordingto claim 1, wherein the film has a length and an electromagneticshielding capability that is retained when the film is strained in atensile mode by 5% of its length.
 11. An article according to claim 1,wherein the film has a length and an electromagnetic shieldingcapability that is retained when the film is strained in a tensile modeby 10% of its length.
 12. An article according to claim 1, wherein thefilm has an electromagnetic shielding capability that is retained whenthe film is bent at a 45° angle.
 13. An article according to claim 1,wherein the film has an electromagnetic shielding capability that isretained when the film is bent at a 90° angle.
 14. An article accordingto claim 1, wherein the film has an electromagnetic shielding capabilitythat is retained when the film is bent at a 180° angle.
 15. Anelectromagnetically shielded article comprising a device or enclosedarea that can cause or is sensitive to electromagnetic interference,wherein the device or area is at least partially surrounded with avisible light-transmissive film comprising a flexible support, anextensible visible light-transmissive metal or metal alloy layer and avisible light-transmissive crosslinked polymeric protective layer. 16.An article according to claim 15, wherein the metal or metal alloy layeris substantially continuous.
 17. A process for transparently shielding adevice or an enclosed area that can cause or is sensitive toelectromagnetic interference, comprising at least partially surroundingthe device or area with a visible light-transmissive film comprising aflexible support, a visible light-transmissive crosslinked polymericprotective layer, and an extensible visible light-transmissive metal ormetal alloy layer sandwiched therebetween.
 18. A process according toclaim 17, wherein the metal or metal alloy layer is substantiallycontinuous, the process further comprising connecting at least onegrounding electrode to the metal or metal alloy layer.
 19. A processaccording to claim 17, wherein the metal or metal alloy layer comprisessilver and the crosslinked polymeric layer comprises an acrylatepolymer.
 20. A process according to claim 17, wherein the film comprisesa base coat layer between the support and the metal or metal alloylayer.
 21. A process according to claim 17, wherein the film comprisesone or more additional metal or metal alloy layers.
 22. A processaccording to claim 17, wherein an interface between the metal or metalalloy layer and an adjacent layer within the film has been subjected toan adhesion-enhancing treatment, or one or more adjacent layers withinthe film comprise an adhesion-enhancing adjuvant, whereby the corrosionresistance of the film is increased.
 23. A process according to claim18, wherein the grounding electrode comprises a tape containing fibersor particles that penetrate the crosslinked polymeric layer.
 24. Aprocess according to claim 17, wherein the film has a perimeter themajority of which is connected to a grounding electrode.
 25. A processaccording to claim 17, wherein the film has a perimeter all of which isconnected to a grounding electrode.
 26. A process according to claim 17,wherein the film has a length and an electromagnetic shieldingcapability that is retained when the film is strained in a tensile modeby 5% of its length.
 27. A process according to claim 17, wherein thefilm has a length and an electromagnetic shielding capability that isretained when the film is strained in a tensile mode by 10% of itslength.
 28. A process according to claim 17, wherein the film has anelectromagnetic shielding capability that is retained when the film isbent at a 45° angle.
 29. A process according to claim 17, wherein thefilm has an electromagnetic shielding capability that is retained whenthe film is bent at a 90° angle.
 30. A process according to claim 17,wherein the film has an electromagnetic shielding capability that isretained when the film is bent at a 180° angle.